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Plant protection

Session 4


Integrated management of diseases on ornamental geophytes and herbaceous perennials

Gary Chastagner (, Hanu Pappu Washington State University, Puyallup, WA, USA

The development and implementation of cost-effective, long-term production practices that rely on an integrated approach to managing diseases is important to enhancing the efficiency of producing field and greenhouse grown ornamental geophytes and herbaceous perennials. While there are numerous economically important diseases that can impact the production of high-quality bulbs, cut flowers, and potted plants, this presentation will focus on approaches that are being used to manage Botrytis diseases on a number of crops, and approaches that are being used to enhance the management of virus diseases on dahlias. Approximately half of the 40 species of Botrytis that have been described cause diseases on ornamental geophytes and flowering herbaceous perennials. These include the generalist B. cinerea, which has been reported on > 1,400 plant species spanning nearly 600 genera, as well as species that have narrow host ranges and are often highly virulent on their host. Fungicides have historically been used extensively in disease management programs to limit the pre- and post-harvest impact of Botrytis diseases. An overview of the effectiveness of new reduced-risk fungicides and biological-based products and approaches, such as the use of environmental-based decision support systems and crop phenology-based application strategies, that are being used to significantly reduce fungicide use will be discussed. Fresh-cut dahlia flowers are an important crop, especially to small specialty cut flower growers that sell flowers to local markets. More than 10 viruses are known to infect dahlias and U.S. stakeholders have identified viruses as their number one plant health concern. A combination of improved diagnostic tools to detect multiple viruses in a single test and the production and strategies for use of virus-free planting material to reduce the impact dahlia viruses will be discussed.

Keywords: Botrytis, dahlias, disease management, viruses


Advances in powdery mildew and rust control for ornamental perennial crops

Mary Hausbeck (, Ethan Tippett, Carmen Medina-Mora, Cheryl Engfehr, Blair Harlan

Michigan State University, East Lansing, MI, USA

Ornamental perennial crops are threatened by obligate fungal pathogens that cause unsightly disease and impact plant vigor. The powdery mildew fungus (Golovinomyces (syn. Erysiphe) cichoracearum DC.; Podosphaera sp.; Oidium sp.) forms a hyphal network across the leaves, flowers, and stems resulting in white, talcum-like colonies. As the disease progresses, lower leaves drop and the plant ceases to produce flowers, becoming unmarketable. Powdery mildew is a common and destructive foliar disease of gerbera daisy (Gerbera jamesonii), dahlia (Dahlia hortensis), aster (Aster sp.), and phlox (Phlox paniculata). The rust pathogen, Puccinia malvacearum, infects hollyhock (Alcea rosea) and mallow (Malva sylvestris) causing light yellow-orange spots on the leaves which then progress to brown pustules; severe disease causes leaf death. This study investigated plant protection products for their ability to limit these diseases under greenhouse or growth chamber conditions. Floral crops known to be susceptible to powdery mildew or rust were inoculated by exposing them to naturally infected plants of the same type. Plants were incubated under high relative humidity conditions. Prior to inoculation, plant protection products were applied as a foliar spray using a hand-pump compressed-air sprayer and reapplied at specific intervals. Assessment included the number of powdery mildew colonies or rust pustules and/or a disease severity rating. Data were analyzed using SAS PROC GLM and statistical differences were compared using the Fisher’s Protected Least Significant Differences or Student-Newman-Keuls test (P=0.05). Experimental trial results indicate that the following plant protection products effectively limited powdery mildew compared to the control: azoxystrobin + benzovindiflupyr, metconazole, myclobutanil, boscalid, trifloxystrobin, pyraclostrobin + boscalid, triflumizole, fludioxonil + cyprodinil, and azoxystrobin. Effective products for rust protection included pyraclostrobin + boscalid, triticonazole + pyraclostrobin, mefentrifluconazole, and myclobutanil. Successful management of powdery mildew and rust in ornamental perennial crops requires integration of this latest research with sanitation and environmental control strategies.

Keywords: disease control, fungicide, pest management


How to deal with non-persistently aphid-transmitted bulb flower viruses?

Martin Verbeek (, Ineke Stijger, Iris Stulemeijer, Frank Kreuk 

Wageningen University and Research, Wageningen, Netherlands

The BKD (the Flower Bulb Inspection Service), Lisse, Netherlands 3VERTIFY, ND Zwaagdijk, Netherlands

Plant viruses which are transmitted by aphids in a non-persistent manner are of high importance to vegetatively propagated crops such as flower b ulbs. I n the N etherlands, a comprehensive quality system is in place consisting of field inspections and laboratory tests on leaves and bulbs, carried out by the Dutch Flower Bulb Certification Agency (Bloembollenkeuringsdienst, BKD). In recent years, infections with viruses which are non-persistently transmitted by aphids, such as the potyviruses Tulip breaking virus (TBV) and Lily mottle virus (LMoV), increased considerably. Growers intend to keep the number of virus sources, which are present in their bulb stocks, as low as possible. Besides virus sources, the other key role players in virus infections are the virus vectors: for potyviruses these are aphids. In the Netherlands, we observed an increase in numbers of flying aphids after mild winters. Moreover, the aphids tend to fly earlier in the year. Chemical crop protection is difficult to use for prevention of non-persistent virus transmission. Moreover, there is a tendency to abolish chemical crop protection products, resulting in a need for alternative measures for aphid and virus control. Our research is focusing on the factors influencing the shift of aphid flights towards early spring, monitoring techniques for aphids and the viruses they are carrying, and the development of environmental-friendly control measures.

Keywords: aphids, non-persistent transmission, plant viruses


Characterization of biological and synthetic microstructures of Zantedeschia leaf surface, and their interaction with Pectobacterium

Iris Yedidia (, Nofar Hod, Preeti Patel, Maya Kleiman Agricultural Research Organization, The Volcani Institute, Bet-Dagan, Israel

Surface architecture and its effect on bacterial attachment, colonization, and micro- environment, are a subject of clinical as well as agricultural interest. The surface microstructure is an essential component of the complex interaction between leaf surfaces and bacterial cells. Our hypothesis proposes that leaf microstructure plays an important role in bacterial behavior, and may strongly affect the outcome of bacterial leaf interactions. To answer this question, two closely related ornamental species of the genus Zantedeschia were chosen as model plants. These natural hosts of Pectobacterium, the agent of soft rot disease, differ in their innate susceptibility to the bacterial pathogen. While Z. aethiopica (ZA) is fairly resistant, the colored hybrid cultivar ‘Captain Romance’ (CR) is highly sensitive. ZA holds a relatively smooth abaxial leaf surface, while CR has a rougher lower surface, which is more competent for bacterial attachment. In order to isolate the effect of the surface microstructure, we produced biomimetic replicas of the differing Zantedeschia surfaces and exposed them to bacterial cells. This allowed us to associate the attachment patterns and the leaf microstructure, and establish a direct linkage between bacterial behavior and the leaf topography. The effect of the microstructure on the microenvironment will also be discussed. Our research combines multidisciplinary approaches such as biomimetics, microscopy, and molecular microbiology to study the events that affect microbes’ interaction with natural and artificial surfaces.

Keywords: biomimetic, leaf surface, microstructure, Pectobacterium, Zantedeschia spp.


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